We propose to investigate: 1. The autoregulation of insulin secretion in normal and obese-hyperglycemic (ob/ob) mice, with particular reference to the possible role of proinsulin and of the C peptide. 2. The secretion of pancreatic glucagon and of growth hormone in human babies during the first 24 hours of life. 3. The secretion of gut glucagon in normal and depancreatized dogs with special reference to the role of pancreatic glucagon and of insulin. 4. The secretion of glucagon by isolated pancreatic islets of obese-hyperglycemic mice. 5. The autoregulation of growth hormone secretion and othr endocrine and metabolic changes in rats with the Mt-T-W-15 tumor.